<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>index首页</title>

    <style>
      html,
      body {
        margin: 0;
        padding: 0;
        height: 100%;
        background-image: linear-gradient(to bottom right, red, gold);
      }

      .box {
        width: 400px;
        height: 250px;
        background-color: rgba(255, 255, 255, 0.6);
        border-radius: 6px;
        position: absolute;
        left: 50%;
        top: 40%;
        transform: translate(-50%, -50%);
        box-shadow: 1px 1px 10px #fff;
        text-shadow: 0px 1px 30px white;

        display: flex;
        justify-content: space-around;
        align-items: center;
        font-size: 70px;
        user-select: none;
        padding: 0 20px;

        /* 盒子投影 */
        -webkit-box-reflect: below 0px -webkit-gradient(linear, left top, left
              bottom, from(transparent), color-stop(0%, transparent), to(rgba(250, 250, 250, 0.2)));
      }
    </style>
  </head>

  <body>
    <div class="box">
      <div id="HH">00</div>
      <div>:</div>
      <div id="mm">00</div>
      <div>:</div>
      <div id="ss">00</div>
    </div>

    <script>
      window.onload = function () {
        // 定时器，每隔 1 秒执行 1 次
        setInterval(() => {
          var dt = new Date()
          var HH = dt.getHours()
          var mm = dt.getMinutes()
          var ss = dt.getSeconds()

          // 为页面上的元素赋值
          document.querySelector('#HH').innerHTML = padZero(HH)
          document.querySelector('#mm').innerHTML = padZero(mm)
          document.querySelector('#ss').innerHTML = padZero(ss)
        }, 1000)
      }

      // 补零函数
      function padZero(n) {
        return n > 9 ? n : '0' + n
      }
    </script>
  </body>
</html>
